I'm trying to compile FFmpeg 4.0 for Android using clang
from the NDK (r18.1.5063045). My host architecture is Mac OS.
Here's my configure command:
./configure \
--target-os=android \
--arch=armv7-a \
--enable-cross-compile \
--cc=${ANDROID_NDK}/toolchains/llvm/prebuilt/darwin-x86_64/bin/clang \
--enable-shared \
--disable-static
This completes successfully. So I run make -j8
and get the following error:
In file included from libavfilter/vf_mestimate.c:22:
In file included from ./libavcodec/mathops.h:40:
./libavcodec/arm/mathops.h:90:26: error: invalid instruction mnemonic 'itt'
"cmp %1, %2 \n\t"
^
<inline asm>:3:2: note: instantiated into assembly here
itt gt
^~~
Any idea what could be causing this?
I suspect Clang is targeting the host OS rather than arm32. Using a standalone toolchain fixes that problem. I noticed that the build system was still using my host strip
tool (which can't handle the arm binaries), so I fixed that by passing --strip
to ffmpeg's configure script.
${ANDROID_NDK}/build/tools/make_standalone_toolchain.py \
--arch arm --api 16 --install-dir /tmp/standalone-toolchain
./configure \
--target-os=android \
--arch=armv7-a \
--enable-cross-compile \
--cc=/tmp/standalone-toolchain/bin/clang \
--strip=/tmp/standalone-toolchain/bin/arm-linux-androideabi-strip \
--enable-shared \
--disable-static
make -j...
The build then failed with an error in libavdevice/v4l2.c:
CC libavdevice/v4l2.o
libavdevice/v4l2.c:135:9: error: assigning to 'int (*)(int, unsigned long, ...)' from incompatible type
'<overloaded function type>'
SET_WRAPPERS();
^~~~~~~~~~~~~~
libavdevice/v4l2.c:121:17: note: expanded from macro 'SET_WRAPPERS'
s->ioctl_f = prefix ## ioctl; \
^ ~~~~~
/tmp/standalone-toolchain/bin/../sysroot/usr/include/bits/ioctl.h:56:5: note: candidate function has type mismatch at 2nd
parameter (expected 'unsigned long' but has 'unsigned int')
int ioctl(int __fd, unsigned __request, ...) __overloadable __enable_if(1, "") __RENAME(ioctl);
^
/tmp/standalone-toolchain/bin/../sysroot/usr/include/bits/ioctl.h:36:5: note: candidate function has type mismatch at 2nd
parameter (expected 'unsigned long' but has 'int')
int ioctl(int __fd, int __request, ...);
^
There's disagreement about the type of ioctl's second parameter. glibc declares it with type unsigned long
:
int ioctl(int fd, unsigned long request, ...);
POSIX and Bionic (and musl) declare it with int
:
int ioctl(int fildes, int request, ... /* arg */);
A similar problem happened with PulseAudio and musl, so I applied the same kind of fix to ffmpeg:
diff --git a/libavdevice/v4l2.c b/libavdevice/v4l2.c
index 10a0ff0dd6..1b9c6e760b 100644
--- a/libavdevice/v4l2.c
+++ b/libavdevice/v4l2.c
@@ -95,7 +95,11 @@ struct video_data {
int (*open_f)(const char *file, int oflag, ...);
int (*close_f)(int fd);
int (*dup_f)(int fd);
+#ifdef __GLIBC__
int (*ioctl_f)(int fd, unsigned long int request, ...);
+#else
+ int (*ioctl_f)(int fd, int request, ...);
+#endif
ssize_t (*read_f)(int fd, void *buffer, size_t n);
void *(*mmap_f)(void *start, size_t length, int prot, int flags, int fd, int64_t offset);
int (*munmap_f)(void *_start, size_t length);
Afterwards, the project built successfully.
FWIW: The project also built for arm64 using these changes:
--arch arm64
--api 21
--arch=aarch64
--strip=/.../aarch64-linux-android-strip